1. Field of the Invention
The present invention relates generally to stopper structures for engine mounts, more particularly to such a stopper structure in which a rubber stopper formed independently and secured press-fit onto an abutting member connected to one of two mounting members of an engine mount, without being adhesive to a superficial surface of the abutting member.
2. Description of the Related Art
An engine mount has been widely used for elastically mounting or hanging a power unit of an automotive vehicle on or from a body of the vehicle in a vibration damping fashion. Generally, such an engine mount includes a rubber elastic body elastically connecting a first mounting member fixable to the power unit, a second mounting member fixable to the body of the vehicle, and an elastic body elastically connecting the first and second mounting members. In the engine mount, a stopper structure is incorporated to limit excess displacement between the first and second mounting members in a direction of vibration input, by bringing an abutting portion connected to the first mounting member into abutting contact with the other abutting portion connected to the second mounting member, or vice versa. The stopper structure includes a rubber stopper for cushioning an impact and/or noise upon abutment of the abutting portions against each other.
FIG. 13 shows an example of conventional engine mount 200 of fluid-filled type. The engine mount 200 includes a mount body 201 that is mounted to a vehicle body (not shown) via a mounting bracket 203.
The mounting bracket 203 includes a holding portion 209 of cup shape having a bottom 205, and a fixing portion 215 having a pair of legs 211, 211 and a sheet 213 by which the legs 211, 211 are connected together, and on which the bottom 205 of the holding portion 209 is received. The holding portion 209 holds the mount body 201 in a press-fit manner, and the fixing portion 215 is fastened at distal ends of the legs 211, 211 to the body of the vehicle, by means of suitable fastening members.
As shown in FIG. 13, a connector arm 217, which is disposed on the side of the power unit, is inserted into a space 219 defined between the pair of legs 211, 211 and situated below the holding portion 209, and is connected to a mounting shaft 216 of a first mounting member 208 of the mount body 201.
A rubber stopper 221 has an overall rectangular tubular shape corresponding to a transverse cross sectional view of the connector arm 217, and is secured press fit onto an outer surface of the connector arm 217 in a non-adhesion manner, such that the connector arm 217 is elastically inserted into the rubber stopper 221.
An upper portion 221A of the rubber stopper 221 is brought into abutting contact with an abutting portion 223 of the mounting bracket 203, and an lower portion 221B of the rubber stopper 221 is brought into abutting contact with an abutting portion 227 of a sub-frame 229 of the body. With this arrangement, a relative displacement between the first and second mounting members 208 and 209 in the vertical direction is suitably limited. In the rubber stopper 221, the upper portion 221A as well as the lower portion 221B are formed with a flat plate configuration having a substantially constant wall thickness over an entire widthwise direction.
Keeping pace with a recent tendency of upgrading quietness in vehicles, there is an increasing demand for rubber stoppers of stopper structures, like the rubber stopper 221, to enhance its shock absorbing performance while maintaining its durability.
The desired durability of the rubber stopper 221 may be obtained by forming it with the flat-plate shape having a thin and substantially constant wall thickness as shown in FIG. 13. Namely, this arrangement permits that a surface pressure acting on the rubber stopper 221 during its abutting contact against the abutting portions 213, 227, evenly distributes over a wide area of the rubber stopper 221. Therefore, the rubber stopper 221 is free from a local considerable deformation or a local stress concentration, leading to an enhanced durability of the rubber stopper 221.
However, this arrangement gives the rubber stopper 221 undesirable load-deformation characteristics (i.e. spring characteristics recognized in a two dimensional graph) which is skyrocketed at the initial stage of the abutting contact of the rubber stopper 221 against the abutting portions 213, 227.
Alternatively, it may be proposed for ensuring the desired durability of the rubber stopper 221 to provide local abutting portions on the abutting surface of the rubber stopper 221. This makes a feeling of touch of the rubber stopper 221 against each of the abutting portions 213, 227 soft, permitting the rubber stopper 221 to provide a soft stopper performance. However, the local abutting portions are likely to suffer from a relatively large deformation and stress, leading to earlier damages and deteriorations of the local abutting portions, resulting in a low durability and a short lifetime of the rubber stopper 221. JP-A-9-166175 and JP-A-2001-349368 disclose examples of conventional rubber stoppers used in stopper structures in engine mounts of hanging type.
The conventional stopper structure as disclosed in the aforesaid documents may suffer from stress concentration at laterally opposite edge portions of upper and lower portions 221A and 221B, which portions are pressed onto corresponding corners of the connector arm 217. Namely, when the upper and lower portions 221A and 221B of the rubber stopper 221 are brought into abutting contact with the abutting portions 213, 227, respectively, the laterally opposite edge portions of the upper and lower portions 221A and 221B is very likely to undergo outward elastic deformation along the superficial profile of the connector arm 217. With this state, the corners provide resistance to the outward elastic deformation of the laterally opposite edge portions, thus generating stress concentration at the laterally opposite edge portions. This results in cracks or other damages of the rubber stopper 221 at the edge portions, thus deteriorating durability of the rubber stopper 221 and the stopper structure.
As is understood from the foregoing description, the durability and the soft stopper performance of the rubber stopper 221 are contradictory to each other, and it has not yet developed a rubber stopper capable of exhibiting both of a desired durability and soft stopper performance.